1. Field of the Invention
The present invention relates in general to collapsible spacers adapted to be placed between a pair of bearings mounted on an axle or spindle or the like for use as a bearing preloading element, and more particularly to a multi-convoluted collapsible spacer having a low spring rate.
2. Description of the Prior Art
Typically, drive shafts in many applications are rotatably mounted within a gear housing through tapered roller bearings. For example, as illustrated in FIG. 1, a pinion shaft 102 driven by an internal combustion engine through a transmission, is rotatably supported in a differential carrier 104 that forms part of a vehicular drive axle. The pinion shaft 102 has at its inner end a beveled pinion gear 110, which meshes with a beveled ring gear 112 in the carrier 104. The ring gear 112 in turn is connected to a differential mechanism (not shown). Here, the mesh of the pinion gear 110 and the ring gear 112 must be proper, lest the differential mechanism will generate excessive noise and wear rapidly. As shown in FIG. 1, the pinion shaft 102 rotates within the differential carrier 104 on inner and outer tapered roller bearings 106 and 108, respectively, which are mounted in opposition to each other along an axis x of rotation.
Typically, the bearings 106 and 108 are set to a condition of preload, so as to impart rigidity to the shaft 102 (rigidity in the sense that the shaft 102 will rotate in the carrier 104 without any radial or axial play) and eliminate all axial and radial free motion between the shaft 102 and the carrier 104, while still allowing rotation with minimum friction within the carrier 104, thus achieving the proper mesh. However, too much preload will cause the bearings 106 and 108 to overheat and fail prematurely. On the other hand, too little preload may cause the bearings to acquire end play, and this likewise decreases the life of the bearings and introduces radial and axial play into the shaft 102.
The pinion shaft 102 extends through a tubular extension 114 on the carrier 104, the axis of which coincides with the axis x. The shaft 102 adjacent to the beveled pinion gear 110 possesses an inner bearing seat 116 around which the inner bearing 106 fits and an outer seat 118 around which the outer bearing 108 fits. The outer seat 118 is considerably longer than the inner seat 116 and terminates at a shoulder 120, which is located between the two seats 116 and 118. At its outer end, the pinion shaft 102 is provided with threads 122 over which a nut 124 is threaded. Indeed, the nut 124 is turned down against the shaft 102 to clamp the bearings 106 and 108 between a drive flange 126 and the pinion gear 110. The extent to which the nut 124 is turned determines the setting for the bearings 106 and 108.
The nut 124 serves to preload the bearings 106 and 108 by advancing the outer bearing 108 over an outer bearing seat 118 on the pinion shaft 102. Initially, before adjustment, the bearings 106 and 108 exist in a state of end play in which the pinion shaft 102 can move both axially and radially with respect to the differential carrier 104 and, of course, rotate as well. As the nut 124 is turned down over the thread 122 at the end of the shaft 102, it forces the outer bearing 108 along the outer bearing seat 118 of the pinion shaft 102. After a short distance the outer bearing 108 encounters a convoluted collapsible spacer 128, which now becomes snugly lodged between the outer bearing 108 and the shoulder 120 at the end of the seat 118. As the advancement continues, still while the bearings 106 and 108 are in a condition of endplay, the spacer 128 collapses. In time, the rollers of the two bearings 106 and 108 seat against the raceways of their respective cups and cones. This represents a condition of zero endplayxe2x80x94a condition in which the shaft 102 cannot shift axially or radially with respect to the housing 102. But some preload is usually desired to insure adequate rigidity or stiffness in the pinion shaft 102 and desired performance from the gears 110 and 112. Hence, the preload setting for the bearings 106 and 108.
The convoluted collapsible spacers for use as a bearing preloading elements are well known to those skilled in the art. Conventionally, the collapsible spacers have a substantially unitary thickness, and are made of a relatively thin strip of metal that is formed into a band and is then further formed so as to be convoluted or undulating in cross section, and are adapted for being compressed to a yield point of the material from which the spacers are made and which will thereafter compress under a substantially constant load for a substantial distance.
The dash line in the FIG. 2 depicts a graph M showing an axial load F applied upon the conventional collapsible spacer 128 as a function of an axial deformation xcex4 of the spacer, and illustrates graphically the manner in which the conventional spacer performs when it is compressed. Such a spacer, when compressed in the axial direction, will first deform resiliently, like a spring, with the force required to effect the compression increasing substantially linearly with the amount of compression (section A-Bxe2x80x2 of the graph M, as indicated by line 130). At a certain amount of compression, a yield strength (or an elastic limit) of the material of the spacer will be reached (point Bxe2x80x2 of the graph M), and the spacer will thereafter start to undergo plastic deformation and offer substantially constant resistance to deformation up to a point where the spacer commences to flatten out section (from point Bxe2x80x2 of the graph M on, as indicated by line 132). If at point Cxe2x80x2 of the graph M, for example, the axial load applied upon the conventional collapsible spacer is released (e.g. by turned the nut 124 up over the thread 122 of the shaft 102 as shown in FIG. 1), the spacer will expand in the axial direction substantially linearly (section Cxe2x80x2-Dxe2x80x2 of the graph M, as indicated by line 34).
However, the conventional convoluted collapsible spacers have a relatively high spring rate, thus the low amount of xe2x80x9cspring backxe2x80x9d. The term xe2x80x9cspring backxe2x80x9d herein refers to a specific resilient deformation of the collapsible spacer in the direction of the expansion thereof when the axial load applied thereupon is released. As a result, they are very sensitive to wear, and are prone to significant change in the bearing preload during the operation that negatively affects bearing life and pinion position.
Thus, there is a need for a convoluted collapsible spacer having a low spring rate, hence less sensitivity to wear and maladjustment.
The present invention provides a novel low spring rate multi-convoluted collapsible spacer adapted for use as a bearing preloading element. The multi-convoluted collapsible spacer in accordance with the present invention comprises a substantially tubular body compressible in an axial direction thereof from a predetermined free length to a substantially shorter length. The tubular body includes a yielding zone and an elastic zone adjacent to said yielding zone. Each of the yielding and elastic zones has at least one convolution curved in the same radial direction and interconnected with a central convolution curved in the opposite radial direction to the convolutions of the yielding and elastic zones.
Preferably, each of the yielding zone and the elastic zone of the collapsible spacer of the present invention has one convex convolution interconnected with the central concave convolution.
Moreover, in accordance with the present invention, the tubular body of the collapsible spacer of the present invention has a substantially variable thickness in the axial direction. More specifically, an average thickness of the body of the collapsible spacer in the elastic zone is substantially greater than an average thickness of the body in the yielding zone. Such an arrangement provides the collapsible spacer a substantially higher resiliency in the axial direction in the elastic zone than in the yielding zone. As a whole, the novel collapsible spacer has a lower spring rate, as compared to the conventional collapsible spacers, thus larger amount of xe2x80x9cspring backxe2x80x9d.
Furthermore, in accordance with the preferred exemplary embodiment of the present invention, the convolutions of the yielding zone and the elastic zone of the spacer have substantially the same outside diameter.
In the alternative embodiment, an outside diameter of the convolution of the yielding zone is substantially smaller than an outside diameter of the elastic zone of the spacer.
Therefore, the multi-convoluted collapsible spacer in accordance with the present invention represents a novel arrangement of the multi-convoluted collapsible spacer providing less sensitivity to wear and maladjustment that allows reliable bearing preloading and drastically reduces the labor cost of assembling and preloading of the tapered bearings in the various gear mechanisms.